1. Technical Field
The present invention relates to a scanning unit with a scanning plate and an eccentric element, and to a position measuring device with a graduation support, which supports a measuring graduation, and a scanning unit for scanning the measuring graduation.
2. Discussion of Related Art
Scanning units and position measuring devices of this type are employed for measuring distances or angles in production machinery in the field of mechanical engineering, as well as increasingly in the semiconductor industry. Increasingly high demands are made on the position measuring devices. In order to optimize the scanning signals, it is necessary to align the scanning plate so that it matches the measuring graduation of the graduation support. In the process the scanning plate is pivoted in a plane around an axis of rotation. In connection with a linear measuring device, this plane is arranged parallel with respect to the plane of the scale surface to which the measuring graduation has been applied. This alignment is called Moiré adjustment.
A Moiré adjustment is known from DE 39 15 679 A1. Here, the scanning unit is fastened by several screws on a fastening elbow. In addition, an eccentric element is rotatably seated in this fastening elbow for the Moiré adjustment. The scanning unit is pivoted around a pin by rotating the eccentric element.
This arrangement has the disadvantage that separate adjusting elements must be provided in addition to the screws. Moreover, radial play must be provided for each screw in order to permit the degree of freedom in the course of pivoting.